Hepatitis C virus (HCV) is considered to be the major etiological agent of non-A non-B (NANB) hepatitis, chronic liver disease, and hepatocellular carcinoma (HCC) around the world. The viral infection accounts for greater than 90% of transfusion-associated hepatitis in the U.S. and it is the predominant form of hepatitis in adults over 40 years of age. Almost all of the infections result in chronic hepatitis and nearly 20% of infected patients develop liver cirrhosis.
The virus particle has not been identified due to the lack of an efficient in vitro replication system and the extremely low amount of HCV particles in infected liver tissues or blood. However, molecular cloning of the viral genome has been accomplished by isolating the messenger RNA (mRNA) from the serum of infected chimpanzees then cloning using recombinant methodologies. See, Grakoui et al. (1993) J. Virol. 67:1385-1395. It is now known that HCV contains a positive strand RNA genome comprising approximately 9400 nucleotides, whose organization is similar to that of flaviviruses and pestiviruses. The genome of HCV, like that of flavi- and pestiviruses, encodes a single large polyprotein of about 3000 amino acids which undergoes proteolysis to form mature viral proteins in infected cells.
Cell-free translation of the viral polyprotein and cell culture expression studies have established that the HCV polyprotein is processed by cellular and viral proteases to produce the putative structural and nonstructural (NS) proteins. At least nine mature viral proteins are produced from the polyprotein by specific proteolysis. The order and nomenclature of the cleavage products are as follows: NH2-C-E1-E2-NS2-NS3-NS4A-NS4B-NS5A-NS5B-COOH. The three amino terminal putative structural proteins, C (capsid), E1, and E2 (two envelope glycoproteins), are believed to be cleaved by host signal peptidases of the endoplasmic reticulum (ER). The host enzyme is also responsible for generating the amino terminus of NS2. The proteolytic processing of the nonstructural proteins is carried out by the viral proteases: NS2-3 and NS3, contained within the viral polyprotein.
The cleavages occurring at NS4A/4B, 4B/5A, 5A/5B sites occur in a trans enzymatic reaction. Additionally, experiments using transient expression of various forms of HCV NS polyproteins in mammalian cells have established that the NS3 serine protease is necessary but not sufficient for efficient processing of all these cleavages. Like flaviviruses, the HCV NS3 protease also requires a cofactor to catalyze some of these cleavage reactions. In addition to the serine protease NS3, the NS4A protein is absolutely required for the cleavage of the substrate at the NS3/4A and 4B/5A sites and increases the efficiency of cleavage of the substrate between 5A/5B, and possibly 4A/4B.
Each of these proteins is key to the viral replicase complex, enabling the virus to replicate its RNA genome and produce progeny viruses. Thus there is a need for the development of inhibitors of these proteins. The present invention provides compounds that are useful in inhibiting NS5B function through covalent modification of a cysteine residue in NS5B.
The present invention provides, inter alia, compounds, compositions and methods that are useful for treating viral infections and associated diseases, particularly HCV infections and associated diseases. The compounds of the invention inhibit viral replication, preferably HCV replication. The compounds are those of formulae I, II, III, IV, V, VI, and VIIa and VIIb, described in detail below.
The methods of the invention comprise administering to an infected or susceptible host a therapeutically or prophylactically effective amount of a compound of formulae I, II, III, IV, V, VI, and VIIa and VIIb, or a pharmaceutically acceptable salt or prodrug thereof.